Image or document information, as is commonly communicated through a network or internet system, is ultimately appreciated by system users through electronic display or physical printing of the document onto a piece of paper by a marking engine like a printer. The spacing of such devices over large networks presents a need for accuracy and consistency in the device operation. Accordingly, the calibrating of such devices, especially for color imaging, is a regular occurrence. The subject invention is particularly directed to facilitating the calibrating processes for such devices, particularly printers.
Document Processing Systems (“DPS”) refers to a set of devices that construct, produce, print, translate, store and archive documents and their constituent elements. Such devices include printers, scanners, fax machines, electronic libraries, and the like. The present invention addresses situations particularly relevant to printing systems and discusses them as the prime example of a DPS, but the present invention should not be construed to be limited to any such particular printing application. Any DPS is intended to benefit from the advantages of this invention.
A printer is typically calibrated by providing a preselected set of target input signals, e.g., a selected set of CMYK signal values, to be processed by the printer and generating outputs corresponding to the inputs. Measurement of the output colors is performed for determining the calibrating function of the DPS so that the input signals are appropriately adjusted for the DPS to output the precisely desired output colors. In other words, the characterization operation of a printer must be determined so that the appropriate mapping function is defined for converting the desired output color to an appropriate input signal. Such calibrating operations and function determinations are well known in the art, and need not be discussed in detail herein, except to note that the programmed software that executes the computation of the appropriate calibration function, requires accurate correspondence between the test target input signals, and the measured device output signals.
Prior art systems have several disadvantages. An incorrect ordering is detected only as a generic inconsistency in measurements and not specifically as an ordering error. For correction, the user is asked to make fresh measurements which is a time consuming and rather boring task. In a closely coupled environment, the possibility of mis-orientation on the measurement stage can be somewhat reduced by providing suitable control files and specific instructions for the users' measurement stage. In a more distributed environment (for example in providing color characterization services over the web), however, this level of support/documentation for a wide variety of color measurement instruments is rather difficult.
The problem addressed by this invention and commonly encountered in the calibration process, is that when a test output is generated for a color characterization/calibration process, the input signals are known, as well as how those input signals were converted and printed out on a piece of paper, precisely because the system controls the printout based upon the input signals. However, the measurement process is not known. The system cannot control how a user actually measures the system output, i.e., the orientation of the output document and which measurement algorithm was employed for the measurement process.
FIGS. 1(a)–1(h) and 2 illustrate an exemplary output document, comprised of a plurality of output elements 20 each corresponding to a different test target element of the input target, wherein eight possible different measurement orders are shown. The measurement process is usually automated by placing the output document onto a measurement platen 30 so that a measurement head 34 moves mechanically across the page to hit and measure the color of each output patch element. It is clear from the different measurement orders of FIG. 1, that the same set of output patches can be measured in many different orders, depending on the control exercised in the measurement stage. However, computation of the calibrating function requires an accurate correspondence between the particular order of printing and measuring. A mismatched correspondence precludes the calibrating software from computing whatsoever the calibrating function.
When an “incorrect” order of measurement is performed so that the calibrating function cannot be computed, prior art systems handled the problem by introducing integrity checks which detected the incorrect measurement order, and then required the operator to re-measure the output document, which, as noted above, would require additional work and time from the operator. The incorrect order of measurements typically resulted from the operator somehow “flipping” the output document to a mis-oriented position, or also when the application of the control algorithm utilized an incorrect order of measurement of the output patch elements.
The subject invention particularly obviates the re-measurement process even after an incorrect measurement order is performed, by taking advantage of the fact that all the appropriate data for computing the calibrating function is available. The incorrect order of measurement can be re-ordered into a correct order of measurement. The possible discrepancies between the orders of measurements can be expected by the characterization software, and the actual measurement order determined by different possible orientations of the target on the measurement stage and different possible control files defining the measurement order so that the determined order of measurements is correct. By considering the possible mis-orientations of the target and determining, either automatically, or visually, which one corresponds to the target, the invention allows the data to be reordered instead of requiring time-consuming and arduous re-measurements. Additionally, the chances of mis-orientation are reduced by providing methods for guiding the user in orienting the target at measurement time.